Optical semiconductor elements such as light-emitting diodes and organic electroluminescence elements advantageously emit highly bright light with a low power. Attempts have been made to apply the optical semiconductor elements expansively to a multiplicity of applications such as lighting devices and display devices.
Disadvantageously, however, these optical semiconductor elements have low durability against moisture and gases. Such low moisture and gas durability may cause the optical semiconductor elements to have lower brightness and, in some cases, to fail to emit light.
As possible effective solutions to the disadvantage, a variety of techniques are attempted for sealing such optical semiconductor elements with curable resin compositions. In particular, sealing techniques using epoxy resin compositions offer excellent sealing performance and are expected to be promising techniques.
Assume that optical semiconductor elements are sealed with curable resin compositions. In this case, there is a need for curable resin compositions that exhibit low permeability and high gas-barrier properties and do not impair the optical semiconductor elements and any other materials by gases (outgases) derived from the resin compositions.
Patent Literature (PTL) 1 discloses a sealing agent for organic electroluminescence elements. The sealing agent contains 20 to 80 parts by weight of an epoxy compound containing a cycloaliphatic skeleton; and 80 to 20 parts by weight of an epoxy compound containing an aromatic ring. The literature, however, fails to describe a countermeasure against outgases derived from the resin composition.
PTL 2 discloses curable resin composition for sealing organic electroluminescence element. The curable resin composition includes an epoxy resin (A), an epoxy resin (B), a latent photoacid catalyst (C), and a silane coupling agent (D). The epoxy resin (A) contains at least two glycidyl groups per molecule and has a molecular weight of 200 to 7000. The epoxy resin (B) contains at least one glycidyl group per molecule and has a molecular weight of 20000 to 100000. The latent photoacid catalyst (C) is activated upon application of energy rays to generate an acid. The silane coupling agent contains a glycidyl group in molecule. The curable resin composition contains the component (B) in a proportion of 30 to 150 parts by weight per 100 parts by weight of the component (A). The curable resin composition contains the component (C) in a proportion of 0.1 to 10 parts by weight and the component (D) in a proportion of 0.1 to 10 parts by weight per 100 parts by weight of the total of the component (A) and the component (B). However, outgassing from the curable resin composition is not restrained at sufficient level.
PTL 3 discloses a resin composition that is an adhesive for packaging of elements such as organic electroluminescence elements. The resin composition includes an epoxy compound (A), a novolac resin (B), a cationic photoinitiator (C), and a filler (D). The literature, however, fails to describe a countermeasure against outgassing.
PTL 4 discloses a low moisture-permeability resin composition. The resin composition includes a compound (A), a compound (B), and a polymerization initiator (C). The compound (A) contains two or more reactive functional groups (a) per molecule. The compound (B) contains one reactive functional group (b) per molecule and has a molecular weight of 50 to 1000. The resin composition is for use in electronic devices that require low moisture permeability. The literature, however, fails to describe the curability of the resin composition and countermeasures against outgassing.
PTL 5 discloses a curable resin. The curable resin includes an epoxy resin containing a terminal oxirane ring. The curable resin further includes at least one of a cycloaliphatic epoxy resin and an oxcetane-ring-containing compound. The curable resin emits outgases in a large volume because of including these components. PTL 6 discloses an epoxy resin composition including a component having a biphenyl structure. The epoxy resin compositions disclosed in PTL 4 and PTL 6 include a components having a biphenyl structure and emit outgases such as acrolein by catalysts.
Independently, optical semiconductor elements such as light-emitting diodes and organic electroluminescence elements employ fine particles having conductivity (conductive fine particles) typically for the connection of fine electrodes in the elements. Examples of known conductive fine particles for these applications include conductive fine particles disclosed in PTL 5. The conductive fine particles each include a fine resin particle and a metal disposed on the entire surface of the fine resinous particle.
Disadvantageously, the conductive fine particles each include a fine resinous particle and a metal disposed on the entire surface of the particle. This configuration requires a large amount of an expensive metal and leads to a high material cost. In addition, there is a need for a special technique such as electroplating technique and alternate adsorption technique to prepare the conductive fine particles. The special technique requires the use of a special apparatus and/or requires a large number of production steps. This disadvantageously leads to high production cost.
In addition, the metal-coated resinous particles are coated with the metal on the entire surface. This configuration causes the particles to be colored. For imparting conductivity to the resulting resin cured product, the conductive fine particles are formulated in a large amount so as to bring the conductive fine particles into contact with each other in the resin cured product. Under these circumstances, it is difficult to inexpensively obtain a cured product that has both transparency and conductivity.